The disclosure of Japanese Patent Application No. HEI 11-119239 filed on Apr. 27, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an internal combustion engine control apparatus and, more particularly, to a control apparatus and a control method for controlling the rotation speed of an automotive internal combustion engine during an idling steady state (a generally-termed idling state, excluding the rising of the engine rotation speed immediately following startup of the engine, and a coasting state) to a target value.
2. Description of the Related Art
For reduced atmospheric pollution, various automotive technologies have been and are being developed to reduce emissions. In particular, there is a strong demand that the engine rotation speed during the idling state, that is, the idle speed, of the internal combustion engine be appropriately controlled so as not to vary but to conform to a target value, because the idling state of the internal combustion engine frequently occurs during actual driving, and has a great effect on emission quality.
Japanese Patent Application Laid-Open No. HEI 5-222997 discloses an apparatus for controlling the engine idle speed. This apparatus performs feedback control with respect to the amount of intake air (intake air flow) and the ignition timing so as to set the engine rotation speed to a target value during the idle operation. When the intake air flow feedback control system fails, the feedback control based on the ignition timing is performed. During cold engine operation, the feedback control based on the ignition timing is limited.
However, if the intake air flow is changed in a case where an imperfect combustion state occurs during a cold state that follows a cold startup and precedes the completion of an engine warm-up, the combustion state further deteriorates in some cases for the following reasons. That is, an imperfect combustion state occurs during the cold state because fuel spraying becomes imperfect so that fuel deposits on intake port wall surfaces or the like and, therefore, a sufficient amount of fuel is not introduced into the combustion chamber. In such a case, the air-fuel ratio shifts to the fuel-lean side. If the throttle opening is enlarged to increase the intake air flow and therefore increase the engine torque, the negative pressure in the intake pipe decreases, so that the fuel spraying quality further deteriorates. The air-fuel ratio thus further shifts to the lean side.
In order to properly control the engine idle speed so as to conform to a target value, it is critical to precisely detect the above-described situation. However, no description regarding such detection or the like is disclosed in the aforementioned laid-open patent application.
Accordingly, it is an object of the invention to provide a control apparatus and a control method of an internal combustion engine that are capable of precisely detecting the occurrence of an imperfect combustion state during feedback control of the engine idle speed.
To achieve the above and other objects of the invention, a control apparatus of an internal combustion engine in accordance with one aspect of the invention includes a plurality of feedback control means for controlling an engine idle speed to a target value, a selection means for selecting optimal feedback control means from the plurality of feedback control means in accordance with a condition, and for controlling the idle speed by using the optimal feedback control means selected, and a determination means for determining that an imperfect combustion state based on the feedback control means selected by the selection means has occurred, if during a feedback control of the idle speed performed by the feedback control means selected by the selection means, an engine speed change-to-control amount change ratio that is a degree of a change in the engine speed with respect to a change in an amount of control of the feedback control means, is out of a predetermined range.
The thus-constructed control apparatus of the invention has a plurality of feedback control means capable of controlling the engine idle speed to a target value, and determines whether an imperfect combustion state has occurred during a feedback control of the idle speed performed by a feedback control means selected in accordance with the condition. Therefore, the control apparatus is able to determine whether the selected feedback control means is appropriate or inappropriate under the present condition.
In accordance with second aspect of the invention, a control apparatus of an internal combustion engine includes a plurality of feedback control means for controlling an engine idle speed to a target value, a selection means for selecting optimal feedback control means from the plurality of feedback control means in accordance with a condition, and for controlling the idle speed by using the optimal feedback control means selected, and a first determination means for, during a feedback control of the idle speed performed by the feedback control means selected by the selection means, determining an engine speed deviation that is a deviation of an actual engine speed from a target engine speed, and for, if the engine speed deviation exceeds a predetermined criterion, determining that an imperfect combustion state based on the feedback control means selected by the selection means has occurred.
As in the first aspect of the invention, the control apparatus in accordance with the second aspect of the invention has a plurality of feedback control means capable of controlling the engine idle speed to a target value, and determines whether an imperfect combustion state has occurred during a feedback control of the idle speed performed by a feedback control means selected in accordance with the condition. Therefore, the control apparatus is able to determine whether the selected feedback control means is appropriate or inappropriate under the present condition.
In accordance with third aspect of the invention, a control apparatus of an internal combustion engine includes a plurality of feedback control means for controlling an engine idle speed to a target value, a selection means for selecting optimal feedback control means from the plurality of feedback control means in accordance with a condition, and for controlling the idle speed by using the optimal feedback control means selected, and a first determination means for, during a feedback control of the idle speed performed by the feedback control means selected by the selection means, determination means for determining that the imperfect combustion state based on the feedback control means selected by the selection means has occurred if an adjusted value of control of the feedback control means being operated, the adjusted value having been adjusted in accordance with the engine speed deviation, exceeds a predetermined limit.
The control apparatus in accordance with either one of the first, second and third aspects of the invention may be constructed so that if it is determined that the imperfect combustion state based on the feedback control performed by the feedback control means selected by the selection means has occurred, a predetermined other feedback control means is selected instead of the feedback control means already selected. This construction makes it possible to switch the present feedback control to the feedback control performed by a predetermined other feedback control means if the imperfect combustion state occurs during the present feedback control. Thus, it becomes possible to avoid continuation of the imperfect combustion state caused by the presently selected feedback control means.
In accordance with still another aspect of the invention, there is provided a control method of an internal combustion engine, in which a feedback control means is selected from a plurality of feedback control means, and the selected feedback control means is used to control the idle speed, and an engine speed change-to-control amount change ratio that is a degree of a change in the engine speed with respect to a change in an amount of control of the feedback control means selected is determined during a feedback control of the idle speed performed by the feedback control means selected, and it is determined that an imperfect combustion state based on the feedback control means selected has occurred if the engine speed change-to-control amount change ratio is out of a predetermined range.
In a control method of an internal combustion engine in accordance with a farther aspect of the invention, a feedback control means is selected from a plurality of feedback control means, and the selected feedback control means is used to control the idle speed. Furthermore, an engine speed deviation that is a deviation of an actual engine speed from a target engine speed is determined during a feedback control of the idle speed performed by the feedback control means selected. If the engine speed deviation determined exceeds a predetermined criterion, it is determined that an imperfect combustion state based on the feedback control means selected has occurred.